This invention relates to apparatus for testing the performance of wheels, wheel hubs and hub bearings of vehicles, and more particularly to a test apparatus that imposes a variable or constant load condition on the items being tested that is generally equivalent to the load condition produced during actual road operation.
One well known method for testing a vehicle wheel comprising a tire mounted on a rim, is the rolling test wherein the tire is supported on or against the convex surface of a large diameter drum. During rotation of the wheel against the drum, a load applied to the wheel by the drum causes a reaction force to develop on the tire. The applied load is generally perpendicular to the axis of rotation of the wheel, i.e., a radially directed force, and, in certain instances, a lateral, or axially directed force, generally parallel to the axis of rotation, can also be generated by the drum.
The amount of force imposed on the wheel during the rolling test is normally limited by the strength of the tire. Therefore, it is usually inadvisable to overload the wheel with the intention of shortening the test time because such overload can lead to premature tire failure. In addition, the overload generally does not provide test results that can be correlated with test results under normal load conditions and is therefore an unreliable test mode.
Heat buildup in the tire under the rolling test is generally accompanied by a decline in lateral forces imposed due to a reduction in the coefficient of friction. It is, thus, difficult to maintain constant test conditions during a rolling test. In addition, tire tread wear is often so extensive during the rolling test, that several tires may be required during one type of test. As a result, the rolling test is costly to perform, requires substantial amounts of time to provide usuable test results, and has only a limited range of testing possibilities.
It is, thus, desirable to provide a test apparatus for wheels, wheel hubs, hub bearings and wheel bolts that will not cause premature tire failure under overload conditions, will not cause extensive heat buildup in the tire and offers a variety of loading possibilities to reproduce force conditions equivalent to those generated during actual road operation.
Among the several objects of the invention may be noted the provision of a novel test apparatus for a wheel, a novel test apparatus for a wheel that permits application of any desired load conditions that correspond to wheel forces occurring in actual operation, a novel test apparatus for a wheel that permits overloading of the wheel without causing significant tire wear or premature tire failure, a novel test apparatus for a wheel that permits application of axially directed forces independent of radially directed forces, a novel test apparatus for a wheel that permits testing of rims, wheel hubs, hub bearings and wheel bolts under conditions resembling actual operation, and a novel test apparatus that permits testing of wheels in tandem arrangement under unequal load conditions that substantially duplicate actual operation.
Other objects and features will be in part apparent, and in part, pointed out hereinafter.